Mechanism to engage part time drive system in a moving vehicle

ABSTRACT

The transfer case of a vehicle that can be driven in two-wheel drive or four-wheel drive includes a range speed transmission driveably connected to the output of a multiple speed ratio transmission and adapted to drive the transfer case output shaft. A drive sprocket journalled on the output case is driveably connected by a chain belt to a driven sprocket that is connected to the front driveshaft. The front axle has a differential that transmits power from the front driveshaft to left and right axleshafts when four-wheel drive is selected. Automatic locking hubs driveably connect the front axleshafts to the front wheel assemblies and are adapted to automatically disengage when the front wheels rotate opposite the direction that produced engagement of the locking hubs. The drive sprocket is accelerated from rest to the speed of the output shaft of the transfer case through operation of a magnetic clutch or hydraulic coupling. A hub member engaged with the driven sprocket is moved to a position of potential engagement with the spline teeth on the output shaft when four-wheel drive operation is selected. The splines remain disengaged, however, until the speed of the drive sprocket reaches approximately that of the output shaft; then the splines engage and the sprocket is driven from the output shaft.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to the field of power transmission systems forvehicles, and more particularly, to such systems that transmit power atthe option of the vehicle operator either to a first set of drive wheelsor to first and second sets of drive wheels.

2. Description of the Prior Art

Formerly, in systems that provided only part-time four-wheel drive, avehicle operator had to exit the passenger compartment in order to setthe front wheel hub locks for four-wheel drive operation, then re-enterthe vehicle and move the shift selector that controls the transfer caseto the four-wheel drive position. Later, manufacturers introducedfull-time, four-wheel drive systems that caused the front drivecomponents to rotate continuously, thereby avoiding the need forselectively operated hub locks. Full-time four-wheel drive systems,however, have substantially reduced fuel economy compared to two-wheeldrive systems because a large inertia mass must be continuously rotated.

Recently, automatic hub locks were introduced to eliminate the need forthe operator to exit the vehicle in order to manually engage hub lockson the axle that is driven only part of the time. In some of thepart-time, four-wheel drive systems, the vehicle must be stopped andshifted to four-wheel drive; then automatic hub locks are engaged whenthe vehicle is driven ahead. Hub lock disengagement is accomplished thefirst time the vehicle is moved in the opposite direction provided thetransfer case shift is in the two-wheel drive position.

Still more recently, drive systems have been manufactured that permitshifting from two-wheel drive to four-wheel drive while the vehicle ismoving. In such systems when two-wheel drive is selected, a slidingsynchronizer collar within the front axle assembly disconnects one ofthe front axleshafts from the front differential allowing the ring gearof the differential, the front driveshaft and the transfer case chain toremain stationary while operating in two-wheel drive. However, thesesystems require that the casing, pinion and gears of the differentialand both front axleshafts be driven by the front wheels during two-wheeldrive operation, so loss of efficiency and reduced fuel mileage result.To engage four-wheel drive, the operator moves a shift lever to the4-high position, which action energizes the synchronizer in the transfercase.

The sliding collar within the axle assembly disconnects one axleshaftfrom the differential so that the ring gear of the differential, thedriveshaft, and the transfer case chain remain stationary while thesystem produces two-wheel drive. However, the pinions and gears of thefront differential unit and the front axleshafts rotate with and aredriven by the front wheels during two-wheel drive operation. In order toengage four-wheel drive, the operator moves the shift lever to thefour-wheel drive high speed ratio position. This action energizes thetransfer case synchronizer to driveably connect the front drive shaftand causes it to accelerate to the speed that corresponds to the vehiclespeed. Then a vacuum valve in the transfer case activates a vacuumdiaphram mounted in the engine compartment. The diaphram pulls a cable,which moves the sliding collar in a front axle assembly to connect thedifferential to the previously disconnected front axleshaft. The shiftfrom two-wheel drive to four-wheel drive can be made at speeds of up to55 mph, but during cold weather and under other adverse conditions,where transmission oil viscosity is a factor, the shift must be made atslower speeds in order to keep the effort required to move the shiftlever at a reasonable magnitude. In four-wheel drive operation, shiftsare made between the high speed ratio and low speed ratio provided thevehicle is stopped and the transmission is first shifted to neutral, asis the conventional practice.

In a part-time four-wheel drive system, conventional manual or automaticlocking hubs may be used in connection with the front wheels. When thehubs are unlocked, the front wheels can rotate free of the front drivemechanism. In addition, the chain and sprocket assembly of the transfercase is disengaged by moving a shift lever in order to stop thefront-drive mechanism.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a system fortransmitting power to the drive wheels of a vehicle wherein either oneset or two sets of wheels are driven concurrently.

Another object of this invention permits the vehicle operator to movethe shift lever to the four-wheel drive, high speed ratio position withno gear clash or grinding and with consistently low effort. This isaccomplished independently of the speed at which the lever is moved andof the vehicle speed. The transfer case has an output shaft, whichtransmits power to the rear wheels continuously during operation, adriving member in the form of a chain sprocket, and a driven chainsprocket connected to the driving sprocket by a flexible, endless chainbelt. A lock-up mechanism in the transfer case is movable by operationof the shift mechanismn to an engagement position, where a drivingconnection is produced between the drive sprocket and the transfer caseoutput shaft when their speeds are synchronous or nearly so, and to arelease position where said connection becomes disengaged. A hub issplined to the driving sprocket and adapted for axial movement into andout of engagement with spline teeth carried by the output shaft. A shiftcollar, carried by the hub, is adapted to be moved axially by the shiftmechanism. When the collar is moved rearward, a compression springbiases the hub rearward to a position where the rear face of its splineteeth is brought into contact with the front face of the spline teeth onthe output shaft. When the shift selector is moved to the four-wheeldrive position, the splines of the hub and of the output shaft arebiased by the spring toward an engaged position, but the splines willnot engage until the speed of the driving sprocket approaches or reachesthe speed of the output shaft. When these speeds are equal or nearly so,the splines engage and power is transmitted from the output shaftthrough the hub to the driving chain sprocket. The chain transmits powerto a front output shaft which drives the front axleshafts of the vehiclethrough a differential mechanism mounted coaxially with the frontaxleshafts. When the shift mechanism is moved to the two-wheel driveposition, a retaining ring on the hub moves the collar spline out ofengagement with the output shaft spline, thereby disconnecting thedriving sprocket from the output shaft. When this occurs, only one setof drive wheels is driven through the transfer case from thetransmission and the engine.

The speed of the driving sprocket is accelerated from rest toward thespeed of the output shaft by a magnetic clutch whose coil is energizedwhen four-wheel drive operation is selected through movement of theshift selector. The magnetic field developed by the coil of the magneticclutch operates to rotate the driving sprocket when the collar is movedby the shift mechanism toward the magnetic clutch. This movement alsobrings the adjacent faces of the spline teeth of the collar and outputshaft into contact where they are maintained by a compressed spring.Alternatively, the driving sprocket is accelerated through operation ofa hydraulic coupling whose torus chamber is hydraulically sealed whenfour-wheel drive operation is selected as the shift collar is moved tothe engagement position where the adjacent faces of the spline teeth onthe collar and output shaft are brought into resilient contact.Hydraulic fluid from a pump located in the transfer case provides astream of pressurized fluid to the toroidal chamber of the hydrauliccoupling, in which the radially directed, angularly spaced impellerblades mounted on the output shaft and turbine blades carried on theshift collar are located. When four-wheel drive is selected, the collaris driven hydraulically by the impeller and is accelerated toward thespeed of the output shaft until the speeds of the turbine and of theimpeller are brought within a range where the effect of the compressedspring produces engagement of the hub spine and the output shaft spline.When two-wheel drive is selected, the shift collar is moved to thedisengagement position, where the hydraulic seal of the toroidal chamberformed by the impeller and turbine rotors is opened and the hydraulicconnection between the output shaft and the shift collar is therebydiscontinued.

Automatic locking hubs located at each wheel of the wheel set that isdriven only in four-wheel drive produce a driving connection between theaxleshafts and the wheels without the need for the hub locks to be setmanually for two-wheel drive or four-wheel drive operation. A camfollower is moved axially on the surfaces of fixed and moving camspermitting a clutch ring that is continuously connected to the wheel hubto become driveably connected to the axleshaft. In this way, the wheelsof the vehicle become connected through operation of the lockingmechanism to the axleshafts. When the shift selector is set foroperation in two-wheel drive and the vehicle is driven in the oppositedirection from that which produced hub lock engagement, the cam followermoves inboard on the cam surfaces, thereby disconnecting the hubassembly from the axleshaft. This action permits the axleshafts,differential ring gear, differential casing, pinions, side bevel gears,the front driveshaft, sprockets, and drive chain to be stopped when thevehicle operates in two-wheel drive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of the four-wheel drive system according to thisinvention.

FIGS. 2A and 2B are partial cross sections of the transfer case taken ata horizontal plane through the axis of the output shaft and frontdriveshaft showing a magnetic clutch for accelerating the drivesprocket.

FIG. 3 is a cross section through the axis of a front axleshaft andwheel hub showing the components of the automatic locking hub inposition to begin engagement of the axleshaft to the wheel hub.

FIG. 4 is a cross section similar to that of FIG. 3 showing thecomponents of the automatic locking hub connecting the axleshaft to thewheel hub.

FIGS. 5A, 5B and 5C are partial cross sections taken at a plane thatcontains the axis of the rear driveshaft showing a hydraulic couplingwhose turbine is carried by the collar of the lockup device. FIG. 5Ashows the components in the disengagement position; FIG. 5B shows theengagement position where the driving and driven member are ready to beconnected; FIG. 5C shows the hub connecting the driving and drivenmembers.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring first to FIG. 1, a vehicle with which the device of thepresent invention can be used, includes front and rear sets of wheels10, 12, an automatic or manual transmission 14 for producing multipleforward and reverse speed ratios driven by an engine (not shown), and atransfer case 16 for continuously driveably connecting the transmissionoutput to a rear output shaft 18 and for selectively connecting thetransmission output to a front output shaft 20. Shaft 18 transmits powerto a rear differential 22 from which power is transmitted to the rearwheels 12 through axleshafts 24, 26. The front wheels 10 are driveablyconnected under certain conditions to right and left axleshafts 32, 34to which power is transmitted from the front driveshaft through a frontdifferential 36.

Referring now to FIGS. 2A and 2B, the transfer case 16 includes a casingformed of three parts 38, 40, 42 joined mechanically at mating flangesurfaces. Power from the transmission output shaft 44 is delivered fromthe transfer case to the rear driveshaft 18 and, under certainconditions, to the front driveshaft 20. The transfer case is lubricatedby a positive displacement pump 46 that channels oil flow through anaxially directed bore 48 formed in the rear output shaft. Because thepump turns with the rear output shaft, the vehicle can be towed atnormal road speeds for extended distances without disconnecting thefront or rear driveshafts. Transmission shaft 44 is supported on abearing 48 fitted within the adaptor cover 38 and the forward end of therear driveshaft is supported within the bore of the transmission outputshaft on needle bearings 50.

Shaft 44 is connected by a spline 52 to a sun gear 54, which is incontinuous meshing engagement with a set of planetary pinions 56, eachalso in continuous meshing engagement with a ring gear 58 splined to thefront case half 40.

A set of spline teeth 60 is formed at the inner end of shaft 44 and isadapted to be engaged selectively by a high-low shift selector hub 62.When the hub is moved forward, the spline 64 formed on its inner surfaceengages the outer splined surface 60 of transmission shaft 44. Thehigh-low shift fork 66 is controlled by the vehicle operator throughmanual operation of the high-low range gear shift lever located withinthe passenger compartment of the vehicle. The planet pinion sets arerotatably mounted on needle bearings supported on carrier pins 68supported on the carrier 70. The inner diameter of the carrier arm isformed with a spline 72, which is brought into meshing engagement with aspline 74 formed on the outer surface of the selector hub 62.

When the high-low range selector within the passenger compartment ismoved so that the shift fork 66, to which the range selector isattached, is in its forward position, hub 62 moves forward with the forkso that one portion of its inner spline surface 64 is brought intomeshing engagement with spline 60 formed on the transmission outputshaft 44, and a second portion of spline 64 remains continuously engagedwith the spline 76 formed on the outer surface of the rear driveshaft18. In this position, the transmission is directly connected to the reardriveshaft 18 and the transfer case is set for operation in the highspeed ratio range.

When the range selector moves shift fork 66 rearward, hub 62 moves withthe fork to the position where clutch teeth 74 engage clutch teeth 72formed on the carrier. In this position, shaft 44 drives sun gear 54through spline 52 and carrier 70 revolves about the axis of shaft 44because ring gear 58 provides a fixed surface upon which the planetpinion sets rotate. Carrier 70 transmits power in a low speed ratiorange through the engaged clutch teeth 72, 74 and from the hub throughthe engaged splines 64, 76 to rear driveshaft 18. When the shiftselector lever is in the neutral position, fork 66 is in the positionshown in FIG. 2A and the rear driveshaft is driveably disconnected fromthe transmission output because neither spline 60 nor clutch 72 isdriveably connected to hub 62.

Journalled on the output shaft is a drive sprocket 77 having teeth 78 incontinuous engagement with an endless, flexible chain belt 80, which isengaged also by the teeth 82 of a driven sprocket 84 that is splined toshaft 86. Sprocket 76 has an outer spline surface 88 on which a lock-uphub 90 and clutch plate 92 are driveably connected and mounted forsliding movement toward the coil assembly of a magnetic clutch 94.Clutch hub 96 is splined at its inner diameter to drive shaft 18 and atits outer diameter 104 to a mating spline of the clutch coil housing 98,which provides a planar surface facing clutch plate 92.

Located within the clutch coil housing 98 is a coil of electrical wire100 wound about the axis of the output shaft and nested within coil ring102, which is joined mechanically to the transfer case 42. The spline104 on the outer surface of the clutch hub 96 is aligned with the spline88 formed on the driving sprocket 77. Therefore, as lock-up hub 90 ismoved axially on spline 88, its spline can be moved into engagement withspline 104 of the clutch hub while remaining engaged with spline 88 ofthe drive sprocket 76. A retention ring 108 fixed to hub 90 is urgedagainst plate 92 by a conical coiled spring 106. As the plate is movedrightward by fork 110, spring 106 is compressed, coil 100 is energizedand the bevel faces 112, 114 on the adjacent ends of splines 91, 104,respectively, are brought into resilient contact. This is the engagementposition. The force developed by the magnetic field induced by the coilacts to accelerate collar 92, which causes sprocket 76 to acceleratetoward the speed of the shaft 18. When the speed of sprocket 76approaches the speed of shaft 18, spring 106 forces hub 90 rearward whenthe teeth of spline 104 align with the spaces between the spline teethon the inner surface of the hub. In this position, hub 90 driveablyconnects shaft 18 to sprocket 76. Forward movement of shift fork 110 hasthe effect of moving splines 91 and 104 out of contact or engagementbecause retention ring 108 causes collar 92 and hub 90 to move as a unitin that direction.

Shaft 86 is supported on the transfer case portions 40, 42 in ballbearings 116 and needle bearings 118. The angularly disposed frontoutput shaft 20 is connected by a Cardan joint 120 to the end of shaft86.

Referring now to FIGS. 3 and 4, the automatic locking hubs 28 that lockthe hub and wheel assembly to the front driving axleshaft 32, 34 areshown in the disengaged and engaged positions, respectively. Whenreleased, the associated front axleshaft is disengaged from the hub bodyassembly 122 and the hub and wheel assembly rotates freely on taperedroller bearings 126 supported on the spindle 124.

The automatic locking hub includes a hub body 122, an inner drive gear128 splined to the axleshaft 32, and a bearing 130 for supporting body122 in rotation on the axleshaft. On the outer surface of inner drivegear 128 there is a first spline 132 and a second spline 134 axiallyspaced from the first spline. A clutch ring 136 has spline teeth formedon its inner surface, which is moved axially into and out of engagementwith the spline 134 of the inner driving gear, and has an outer splinesurface that is continuously engaged with the spline 138 formed on theinner surface of the body. The recesses between spline teeth on theouter surface of the clutch ring accommodate three angularly spaced legs140 of a clutch ring cage and permit these legs to extend axially fromthe inboard ring portion 142 of the clutch ring cage to the free ends ofthe legs at the outboard end of the cage. A cage spring 144 iscompressed between ring portion 142 and clutch ring 136, the springapplying an outwardly directed force to the clutch ring tending toproduce engagement of its internal spline with spline 134 of the innerdrive gear. A clutch ring retainer cap 146 has an axial surface at itsinboard face that contacts the adjacent face of the clutch ring undercertain conditions and is retained in position at its outboard side bythe outboard free end of the axially extending legs 140 of the cage. Amain spring 148 is compressed between the inner surface of the hub bodyand an inclined surface at the free end of the cage leg.

A cam follower 150 is formed with an internal spline 152, which movesinto and out of engagement with the splines 132 of the inner drive gear128, and has three angularly spaced legs, which contact ramp surfaces ona fixed cam 154 and on a moving cam 156. The outboard face of the camfollower abuts the inboard face of the clutch ring cage and the force ofmain spring 148 maintains these surfaces in contact throughout theoperation of the locking hub. The force of the spring holds the inboardend of the legs of the cam follower in contact with the cam surfaces ofcams 154, 156. The fixed cam 154 is keyed to the spindle 124 and has sixlegs angularly spaced about the axis of the hub, each leg being formedwith a pair of oppositely inclined cam surfaces, which are engaged bythe cam follower. Each leg of the fixed cam has a first inclined surfacehaving one direction component parallel to the axis of the hub assemblyand a second component directed tangentially. At the interior end of thefirst surface of the fixed cam is an intersecting second cam surfacehaving axial and tangential direction components, its tangentialcomponent being larger than its axial component, equal to the tangentialcomponent of the first inclined surface, but of the opposite sense ofdirection.

The moving cam 156 is mounted on the outer cylindrical surface ofspindle locknut 58, which is threaded on the spindle 124 so that thelocknut and spindle rotate as a unit. A thrust bearing 160 and washer162 are located between the flange of the locknut and the moving cam inorder to facilitate relative rotation between them. Moving cam 156 isformed with three angularly spaced pockets, each pocket having anincluded angle about the hub axis of approximately 60 degrees into whichare fitted friction shoes 164, which contact the outer cylindricalsurface of the locknut and are biased against that surface by gartersprings 166. Located between each pocket on the moving cam are threeangularly spaced legs directed outboard from its inboard end, each legbeing formed with first and second inclined cam surfaces, each havingaxial and tangential direction components. The direction components ofthe cam surfaces of each leg include axial components having the samemagnitude and sense of direction and tangential components having thesame magnitude but opposite sense of direction. Formed on each movingcam leg and located midway between the circumferential extremity of eachleg at the intersection of the first and second cam surfaces of each legis a boss that forms a stop surface and against which the cam followermakes contact as it rotates relative to the moving cam. After the camfollower contacts the boss of the moving cam, the cam follower andmoving cam rotate as a unit provided the direction of rotation is suchthat the cam follower and boss maintain contact. However, when thedirectional sense of rotation changes, the cam follower disengages theboss and relative rotation between the moving cam and cam follower ispossible.

When the front driveshaft 20 is driven by the chain belt 80 after thetransfer case is disposed for four-wheel drive operation, the frontaxleshafts 32 are driven by the differential mechanism 36. In FIG. 3,spline 152 of the cam follower is located adjacent spline 132 of theinner drive gear and engagement of these splines occurs when the camfollower is moved outboard by the cam surfaces due to rotation ofaxleshaft 32. The axleshaft is driven by the front differential, theinner spline 170 of the clutch ring is disengaged from spline 134 of theinner drive gear, but it is located in position for engagement as thecam follower and clutch ring is moved outboard. As the front axleshaftsbegin to rotate, the inner drive gear and the cam follower rotate withthe axleshafts. The cam follower moves up the ramps of the fixd cam, andcauses the cam follower and clutch ring cage 140 to move outboard,thereby compressing cage spring 144 and causing the outboard face ofsplines 170 to abut the inboard face of splines 134. The clutch ringwill not engage the inner drive gear until the spline teeth becomealigned, but after the splines are aligned, the cage spring produces theengagement shown in FIG. 4. When the clutch ring and inner drive gearsplines are aligned, the clutch ring engages the inner drive gear,thereby producing a driveable connection between the axleshafts 32 andthe hub body 122. The wheel assembly is mounted on a flange 172 and thefront wheel 10 is driven from the axleshaft.

When the cam follower has moved to the outboard end of the fixed camsurface, further rotation causes the cam follower to move from thesurface of the fixed cam onto the surface of the moving cam as shown inFIG. 4. In this position, the cam follower is held away from thesurfaces of the fixed cam and full engagement of splines 170 and 134 ismaintained.

Disengagement of the locking hub from the axleshaft occurs when thetorque applied to the axleshaft is less than approximately 17 Nm,provided the transfer case is positioned for two-wheel drive operationand the vehicle is moved opposite the direction that producedengagement. When these conditions occur, the front axleshafts 32 are notdriven from the engine, but the hub body 122 is rotated in the oppositedirection from that which produced engagement by the wheel assembly asit rotates in contact with the ground. The clutch ring drives the innerdrive gear and the cam follower moves inboard of the surfaces of themoving cam and fixed cam and is biased in that direction by the effectof the main spring 148. When the cam follower has moved inboardsufficiently far, the clutch ring splines 170 become disengaged from thesplines 134 of the inner drive gear and the hub becomes disengaged fromthe axleshafts.

A hydraulic system for accelerating the sprocket 76 so that the frontdriveshaft 20 can be driven from the chain belt 80 is shown in FIGS.5A-5C. The spline teeth 88 formed on the outer surface of sprocket 76are in continuous meshing engagement with the inner splines 174 of thehub 176, which is adapted to be moved axially rearward into engagementwith the splines 178 of an impeller or driving member 180, driveablyconnected to the shaft 18 at a spline connection 182. A turbine 184 isdriveably connected by a spline 186 to the hub, and a retaining ring 188mounted on the turbine blocks a portion of the rearward movement of thehub relative to the turbine. Shift fork 110 engages the turbine in arecess and moves the turbine axially toward and away from the impelleras the 4WD-2WD shift selector is moved by the vehicle operator. Coilspring 190 biases the hub and turbine in opposite axial directions andtends to keep the hub in contact with the retention ring 188.

The impeller is fitted with multiple impeller blades 192 angularlyspaced one from another in radial planes that extend outwardly from theaxis of shaft 18. Similarly, the turbine carries multiple turbine blades194 spaced angularly from one another and located in radial planesextending from the axis of the shaft 18. A seal 196 carried on theimpeller is adapted to become compressed, as shown in FIGS. 5B and 5C,when the turbine is moved toward the impeller, thereby providing ahydraulic seal at the radially outer end of the toroidal chamber definedby the impeller and turbine in which the blades 192 and 194 are located.

The output port of pump 46 is hydraulically connected to the toroidalchamber through a bore 48 formed in shaft 18 and a check valve 198. Aradial passage 200 is connected to one of several passages 202, 204, 206that are brought into alignment with passage 200 as hub 176 is movedaxially by the shift selector. Check valve 198 permits hydraulic fluidto flow from the pump outlet toward the hydraulic coupling formed by theimpeller 180 and turbine 184 when they are moved to the position shownin FIGS. 5B and 5C, but prevents flow from the coupling toward the pump.

The pump 46 is a radial piston pump supplied with fluid from the sump208 portion of the transfer case through an oil filter 210 and oilpickup tube 212 to the pump body 214, which is located between a frontcover 216 and a rear cover 218. Diametrically opposed pistons are biasedby springs within the body as they rotate and contact a surface that islocated eccentric of the axis of output shaft 18. The eccentricitycauses the pistons to work within the cylinder and to pump oil from thesump to the bore 48 of the output shaft.

In operation, when the 4WD-2WD shift selector is in the neutralposition, the hydraulic device for accelerating sprocket 76 is in thedisengagement position shown in FIG. 5A. Here the pump output flowsthrough check valve 198, passages 200, 202 and through the hydrauliccoupling defined by the impeller and turbine to the sump 209. Radialflow through the hydraulic coupling is permitted because seal 196 is outof contact with the adjacent surface on the turbine.

When four-wheel drive operation is selected, shift fork 110 moves to theengagement position shown in FIG. 5B moving the turbine rearward andcausing seal 196 to become compressed on the inclined surface of theturbine casing, thereby sealing the outer periphery of the torus chamber208. When the turbine moves rearward, the rear face 220 of spline 174 ismoved into contact with the forward face 222 of spline 178. Thesesplines will not engage when the speeds of the turbine and impeller areappreciably different, but they will rotate relative to one another withthe surfaces 220, 222 in contact. This contact prevents further rearwardmotion of a turbine 184, but permits seal 196 to become compressed onthe inclined surface of the turbine sealing the torus chamber. In theengagement position, spring 190 is compressed and applies a force thatbiases hub 176 rearward.

When chamber 208 is sealed, hydraulic fluid from the pump enters andfills the torus chamber through passages 200 and 204. The fluid in thecells between the blades 192 of impeller 180 is forced to rotate withthe impeller and is, therefore, subjected to centrifugal force, whichcauses it to flow radially outward. Initially, turbine 184 is stationaryand there is no centrifugal force on the fluid within it. The fluid inthe impeller, under the influences of centrifugal force, enters theturbine near the outer circumference and forces fluid from the turbineinto the impeller near the inner circumference. Thus, a circulation isset up, which continues as long as there is a difference between thespeeds of the impeller and turbine. In normal operation, the turbinealways turns at a lower speed than the impeller, and since both havesubstantially the same dimensions, the centrifugal force on the fluid inthe impeller always is greater than that of the fluid in the turbine. Itis this difference between the two centrifugal forces that causes thefluid to circulate in the torus. The fluid in the coupling has a dualmotion; it travels with the impeller and turbine around the axis of thecoupling, and it flows around the central core of the torus. Since thearea of the flow path is constant around the torus, there is no changein velocity in the circumferential direction. On the other hand, thevelocity of the whirling motion around the axis of the couplingincreases as the liquid passes from the inlet to the outlet of theimpeller, and decreases as it flows from the inlet to the outlet of theturbine. Since the velocity of the liquid increases in the impeller, itskinetic energy increases there, but this gain in kinetic energy can comeonly from the impeller. Therefore, the impeller encounters resistance asit increases the absolute velocity of fluid in the cells, and it takespower to keep the impeller running against this resistance. In theturbine, the fluid is slowed and presses forward against vanes 194. Whenthe turbine is moving under this force, power is produced. In this way,the rotational speed of the turbine is increased toward the speed ofoutput shaft 18 until a condition is reached that permits splines 174and 178 to become engaged.

When the splines are engaged, the members of the device move to theengaged position shown in FIG. 5C. In this position, spring 190 expandssomewhat and forces hub 176 into contact again with retaining ring 188.Hydraulic fluid is supplied through passage 200 and 206 to the sump andsprocket 76 is driven from the output shaft 18 through spline 182,engaged splines 174, 178, and engaged splines 174 and 88. In this way,power is transmitted to shaft 86 and sprocket 84 by the chain belt 80,and the front driveshaft 20 is driven causing the automatic hub locks toengage and the vehicle to be driven by the axleshafts of the forward andrear wheel sets.

When two-wheel drive operation is selected, shift fork 110 is movedforward to the disengagement position shown in FIG. 5A, therebydisengaging the impeller from the turbine, opening the torus chamber anddriveably disconnecting the front driveshaft 20 from the output shaft18.

Having described a preferred embodiment of my invention, what I claimand desire to secure by U.S. Letters Patent is:
 1. A device fordriveably connecting rotating members comprising:a rotatably mounteddriven member having a first clutch surface; a rotatably mounted drivenmember having a second clutch surface; lockup means movable to anengagement position where the driving member and driven member aredriveably connectable and movable to a disengagement position where saidconnection is prevented, said connection being made when the speeds ofthe driving member and driven member so permit; actuating means formoving the lockup means to the engagement position and to thedisengagement position; means for accelerating the driven member towardthe speed of the driving member and within a range of speed that permitsthe lockup means to connect the driving member and the driven memberwhen the lockup means is moved to the engagement position and forproducing no such acceleration when the lockup means is moved to thedisengagement position; and wherein the lockup means further includes: ahub, having a third clutch surface continuously engaged with either thefirst clutch surface or the second clutch surface, adapted to engageselectively either the second clutch surface of the first clutch surfacewith which the hub is not continuously engaged; a collar adapted to movein accordance with movement of the actuating means; retention means forpreventing movement of the collar relative to the hub in a firstdirection and for permitting movement of the collar relative to the hubin a second direction; and spring means for resiliently biasing the hubtoward the retention means and for resiliently biasing the third clutchsurface into engagement with either the second clutch surface or thefirst clutch surface with which the hub is not continuously engaged. 2.The device of claim 1 wherein the driving member has a first stopsurface facing the hub and the hub has a third stop surface facing thedriving member, the first and third stop surfaces being biased by thespring means into contact to block movement of the hub toward thedriving member, thereby preventing engagement of the first and thirdclutch surfaces when said clutch surfaces are nonaligned for engagementand to permit engagement of the first and third clutch surfaces whensaid clutch surfaces are aligned for engagement.
 3. The device of claim2 wherein the spring means resiliently urges the hub against theretention means, the actuating means moves the collar toward the drivingmember to the engagement position where the third surface is resilientlyheld against the first surface by the spring means until the first andthird clutch surfaces engage.
 4. The device of claim 2 wherein the firststop surface is formed on the end of the first clutch surface that facesthe hub and the third stop surface is formed on the end of the thirdclutch surface that faces the driving member.
 5. The device of claim 1wherein the driven member has a second stop surface facing the hub andthe hub has a third stop surface facing the driving member, the secondand third surfaces being biased by the spring means into contact toblock movement of the hub toward the driven member, thereby preventingengagement of the second and third clutch surfaces when said clutchsurfaces are nonaligned for engagement and to permit engagement of thesecond and third clutch surfaces when said clutch surfaces are alignedfor engagement.
 6. The device of claim 5 wherein the second stop surfaceis formed on the end of the second clutch surface that faces the hub andthe third stop surface is formed on the end of the third clutch surfacethat faces the driven member.
 7. The device of claim 1 wherein thedriving and driven members have concentric axially aligned first andsecond clutch surfaces, respectively, the first clutch surface having afirst stop surface adjacent the third clutch surface;the hub has a thirdstop surface adjacent the first stop surface of the driving member, ismounted coaxially with the driven member and is adapted to slide axiallyalong the second clutch surface thereby bringing the first and thirdstop surfaces into abutting contact, permitting relative rotation of thehub and driving member and preventing engagement of the first and thirdclutch surfaces; and the spring means urges the hub and collar intocontact for unitary movement of the hub and collar as the actuatingmeans moves the collar toward the engagement position, the spring meansbeing adapted to permit axial movement of the collar relative to the hubto the engagement position after the first and third stop surfaces makecontact and to urge the first and third clutch surfaces into engagement.8. The device of claim 7 wherein the driving member has a first stopsurface facing the hub and the hub has a third stop surface facing thedriving member, the first and third stop surfaces being biased by thespring means into contact to block movement of the hub toward thedriving member, thereby preventing engagement of the first and thirdclutch surfaces when said clutch surfaces are nonaligned for engagementand to permit engagement of the first and third clutch surfaces whensaid clutch surfaces are aligned for engagement.
 9. A device fordriveably connecting rotating members comprising:a rotatably mounteddriving member; a rotatably mounted driven member; lockup means movableto an engagement position where the driving member and driven member aredriveably connectable and movable to a disengagement position where saidconnection is prevented, said connection being made when the speeds ofthe driving member and the driven member so permit; actuating means formoving the lockup means to the engagement position and to thedisengagement position; means for accelerating the driven member towardthe speed of the driving member and within a range of speed that permitsthe lockup means to connect the driving member and the driven memberwhen the lockup means is moved to the engagement position and forproducing no such acceleration when the lockup means is moved to thedisengagement position, including a hydraulic impeller driveablyconnected to the driving member, and hydraulic turbine driveablyconnected to the driven member and adapted for selective hydraulic driverelationship with the impeller and means for connecting a source ofhydraulic fluid to the accelerating means; wherein the impeller definesa portion of a chamber in which multiple radial vanes carried by theimpeller and spaced angularly about its axis are located and wherein theturbine defines another portion of the chamber in which multiple radialvanes carried by the turbine and spaced angularly about its axis arelocated, wherein the driving member has a first clutch surface, thedriven member has a second surface and wherein the lockup meansincludes: a hub on which a third clutch surface is formed, continuouslyengaged with the second clutch surface and adapted to engage selectivelythe first clutch surface; a collar adapted to move in accordance withthe movement of the actuating means, carrying the hydraulic turbinewhose portion of the chamber faces the chamber portion defined by thehydraulic impeller; retention means for preventing movement of thecollar relative to the hub in a first direction and for permittingmovement of the collar relative to the hub in a second direction; springmeans for resiliently biasing the hub toward the retention means and forresiliently biasing the third clutch surface into engagement with thefirst clutch surface; and means for hydraulically sealing the chamberdefined by the turbine and impeller when the turbine is moved toward theimpeller.
 10. The device of claim 9 wherein the driving member has afirst stop surface facing the hub and the hub has a third stop surfacefacing the driving member, the first and third stop surfaces beingbiased by the spring means into contact to block movement of the hubtoward the driving member, thereby preventing engagement of the firstand third clutch surfaces when said clutch surfaces are nonaligned forengagement and to permit engagement of the first and third clutchsurfaces when said clutch surfaces are aligned for engagement.